The Field Book for Describing and Sampling Soils describes the specific force that corresponds with each class. A 2.5 to 3.1 cm cube should be used or a plate 1.0 –1.5 cm long by 0.5 cm thick.
The capacity of soil to adhere to other objects such as your fingers. Estimated at moisture content that displays maximum adherence between thumb and fore finger.
Non-Sticky – little or no soil adheres to fingers after release of pressure. Sands typically fall in this category Slightly Sticky – soil adheres to both fingers after release of pressure with little stretching on separation of fingers.
Plasticity classes; Non-Plastic – will not form a 6 mm wire, or if formed , can not support itself if held on end Slightly Plastic – 6 mm wire supports itself, 4 mm wire does not Moderately Plastic – 4 mm wire supports itself, 2 mm wire does not Very Plastic – 2 mm wire supports itself
Consistence and consistency Sadia Bibi Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan 2010
In air dry state consistency is measured by soil’s resistance to rupture or to fragmentation when squeezed. So it is characterized by
Tendency to crush to powder
Inability of crushing material to cohere again when pressed together
Air dry Consistency 1 Newton (N) = 0.224 lb/ft Class Description Loose (sands) Separate from each other when soil is non coherent Symbol L or LO or lo Soft (<8 N) (loams) Soil crushes under very low pressure/ weakly coherent Slightly Hard (8 to < 20 N) Soil material crushes- low pressure - little resistance Mod Hard (20 to < 40 N) Soil material crushes- moderate pressure -resistance Hard (40 to < 80 N) ( clay loam) Soil material crushes under strong pressure Break b/w hands Very Hard (80 to < 160 N) (clays) Can not be crushed between thumb and forefinger but b/w hands with difficulty Extremely Hard Pressure applied by foot with full body or with the help of hammer so depends upon cementation
Estimated at moisture content that displays maximum adherence between thumb and fore finger
Degree a soil can be molded or reworked causing deformation without rupturing. We take soil material in wet condition and roll it b/w thumb and fore finger and then observe whether rod or wire is formed
It is a midway b/w air dry consistency and field capacity
It is resistance to squeezing forces b/w thumb and fore finger
Moist Consistency 1 Newton (N) = 0.224 lb/ft Moist comments Stress Loose Non coherent 0 Very Friable Soil material crushes very easily under very gentle pressure < 8 N Friable (best) Soil material crushes under gentle pressure 8 to < 20 N Firm Under moderate pressure b/w thumb and forefinger 20 to < 40 N Very Firm Strong pressure is required 40 to < 80 N Extremely Firm Can’t crush 80 to < 160 N
Behavior of soil at different water contents is called Atterberg limits
Before building roads and motorway is considered
The state of consistency b/w solid and liquid range has been divided into a number of distinct stages by imposing limits to indicate the soil water content limits for various states of consistency.
Depending on the water content of the soil, it may appear in four states:
In each state the consistency and behavior of a soil is different and thus so are its engineering properties. These limits were created by Albert Atterberg , a Swedish chemist. They were later refined by Arthur Casagrande
• Liquid Limit (LL) Upper limit of plasticity of soil
is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow but posses a small shearing strength.
At this point water film becomes so thick that cohesion is decreased and soil mass flows under an applied stress
• Plastic Limit (PL ) is the state of minimum water contents & defined as the moisture content at which soil begins to behave as a plastic material. At that state soil has the property of ploughing. Plastic limit is determined by finding the water contents at which the soil rolled into thread 3mm dia. Begins to break.
• Shrinkage Limit (SL) is defined as the moisture content at which no further volume change occurs with further reduction in moisture content. (SL represents the amount of water required to fully saturate the soil (100% saturation)